Semiconductor light emitting apparatus, preferably light emitting diodes (LEDs), are considered to be an ideal candidate for photo-dynamic-therapy (PDT), photobiostimulation (photobiomodulation), photo-sterilization, photo-curing, and other medical applications due to their long lifetime, high wall-plug efficiency, and low heat generation.
Some examples of prior arts related to LED based medical light emitting apparatus include U.S. Pat. Nos. 5,634,711, 5,698,866, 6,602,275 and PCT patent application No. WO2005/035060. In U.S. Pat. No. 5,634,711, Kennedy et al. disclose a hand-held portable light emitting device for medical and industrial photo-curing and phototherapy applications. The hand-held light emitting device comprises an array of LEDs producing a light intensity in the range of several hundred mW/cm^2. The light beam from the LED array is delivered to the treatment site through a short fiber optic light guide mounted in front of the LED array. In U.S. Pat. No. 5,698,866, Doiron et al. disclose a phototherapeutic light comprising a low-power LED array with high packing density. The LEDs are overdriven to produce a desired light intensity of several hundred mW/cm^2. A direct illumination scheme is employed in the Doiron patent, where the LED array is placed close to the treatment site for light delivery. In U.S. Pat. No. 6,602,275, Sullivan discloses an LED panel comprising thousands of low power LEDs for therapeutic treatment of living organisms. The Sullivan patent utilizes a direct illumination scheme, where the device is intended to lie against the skin or surface, near the skin/surface, and/or from a distance ranging up to several feet from the skin/surface. In PCT patent application No. WO2005/035060, Persin et al. disclose a portable illuminator for photo-dynamic-therapy. An LED cluster is utilized to produce light in one or more desirable wavelengths. The light beam is delivered to the treatment site either through a glass or plastic light guide or through a transparent window.
The light emitting apparatus disclosed in the above-cited references produce a light intensity of <1,000 mW/cm^2 since low power LED arrays are employed, whereas in certain medical applications, a higher light intensity is desirable. The recent development of high intensity LEDs (LED arrays), especially those chip-on-board (COB) packaged LEDs (LED arrays) makes it possible to build light emitting apparatus with higher output intensity and more compact size. However, these LEDs (LED arrays) also bring the problem of increased heat generation and difficulty in light energy delivery due to their large light emitting area and beam divergence angle.
The lack of an efficient and convenient light energy delivery method is a common weakness for the previous disclosed medical light emitting apparatus. The direct illumination scheme employed in the Doiron and Sullivan patents requires the LED array to be placed close to the target object as the LED beam has a large divergence angle. This is inconvenient for some hard-to-reach areas due to the size limitation of the LED array and its supportive components (such as lenses, heat sinks, etc.). More importantly, the heat produced by the LED array will induce significant temperature increase for the treatment site in close contact. To avoid the temperature increase problem, the Kennedy and Persin patents employ glass or plastic fiber optic light guides for light energy delivery. However, the glass or plastic fiber light guides become rigid when their diameter is increased to match with the size of the LED array for efficient light energy coupling. Thus in both the Kennedy and Persin patents, the fiber optic light guide is used as a non-flexible element integrated with the LED array to form a hand-held device. This design is not suitable for high intensity LEDs (LED arrays) as the hand-held device can not provide efficient heat dissipation for the high intensity LEDs. In addition, the fiber optic light guide suffers a filling factor and hot spot issue as it is generally composed of a plurality of optical fibers bundled together where there exist both bright and dark regions when illuminated.